The notoriously smoggy skies of Los Angeles are a little bit cleaner than you might expect, at least in one respect. According to a study announced Aug. 9 by the National Oceanic and Atmospheric Administration (NOAA), the levels of certain vehicle-related pollutants in Los Angeles have dropped by 98% since the 1960s. The study has been accepted for publication in the Journal of Geophysical Research Atmospheres but is not yet available online.

The study looked specifically at vehicle-emitted pollutants called volatile organic compounds (VOCs) which enter the atmosphere from the tailpipes of cars and trucks. VOCs are one of the contributing factors to ground-level ozone, which can be damaging to peoples' lungs as well as to any plants in the area.

The drop in VOCs was most significant between 2002 and 2010, when they were cut in half. This drop was despite the fact that drivers in Los Angeles now use three times as much gasoline and diesel fuel as they did 50 years ago.

So why have VOC emissions fallen so dramatically? "The reason is simple," said the study's lead author, Carsten Warneke, Ph.D., a NOAA-funded scientist with the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder. "Cars are getting cleaner," he said in a prepared release. Contributing factors in the VOC decline cited by the NOAA include catalytic converters, improved engine efficiency, and reformatted fuels that are less prove to evaporation.

This doesn't mean that Los Angeles residents can breathe easier, however. While overall VOCs have dropped, some of the compounds remain at high levels. Propane and ethane, which are emitted by the burning of natural gas and other sources, have not declined as quickly. Another NOAA study recently found that a third VOC, ethanol, is actually increasing.

Meanwhile, although VOCs contribute to ozone, they are not the only factor influencing LA's infamous ozone-laden smog, which still remains the worst in the country, according to the annual State of the Air report from the American Lung Association, which was released this past April.

"Ozone and particle pollution contribute to thousands of hospitalizations, emergency room visits, and deaths every year," Dr. Kari Nadeau, a Stanford Medical School professor and American Lung Association researcher, said when the State of the Air report was released. "Air pollution can stunt the lung development of children, and cause health emergencies, especially for people suffering from chronic lung disease, including asthma, chronic bronchitis, and emphysema. Both long-term and short-term exposures can result in serious health impacts."

The State of the Air report also ranked the Los Angeles-Long Beach-Riverside area as having the third-highest level of annual particle pollution in the nation and the fourth-highest level of short-term particle pollution. But on the plus side, the association did note that LA's air quality was the best it has been since 1999.

A slightly earlier report, published this past February in the Archives of Internal Medicine, linked high smog levels to an increased risk of stroke and memory loss. The study was actually conducted in and reported on air pollution in Boston, but it pointed out that air quality levels even below current standards set by the Environmental Protection Agency still pose risks to people who breathe particulate air pollution. Boston did not even rank in the worst 25 metropolitan areas in the State of the Air report.